Metal halide ionic liquid catalysts are attractive in many refinery process applications where the liquid catalyst is easily mixed with the reactants in a reactor, and readily separated from hydrocarbon products in a settler. Ionic liquid catalysts may be used in a range of hydrocarbon conversion processes, such as paraffin alkylation, paraffin isomerization, olefin isomerization, olefin dimerization, olefin oligomerization, olefin polymerization and aromatic alkylation.
An example of an ionic liquid catalyzed hydrocarbon conversion process is the alkylation of isoparaffins with olefins to make gasoline cuts with high octane number (see, e.g., U.S. Pat. No. 7,432,408 to Timken et al.). In contrast, a widely used conventional process for the alkylation of isoparaffins with olefins is catalyzed by sulfuric acid or hydrofluoric acid. Apart from environmental, health and safety concerns related to the use of large volumes of H2SO4 or HF, ionic liquid catalyzed alkylation offers a number of advantages over conventional alkylation, including: lower capital expenditure on plants, lower operating expenditure, lower catalyst inventory volume, lower catalyst make-up rate, expansion of usable feeds, and higher gasoline yield.
The presence of HCl as a co-catalyst with an ionic liquid provides an increased level of catalytic activity, for example, as disclosed by U.S. Pat. No. 7,432,408. Typically, anhydrous HCl or organic chloride is added with the reactor feed to direct the reactions to the desired activity and selectivity (see, e.g., U.S. Pat. No. 7,495,144 to Elomari, and U.S. Pat. No. 7,531,707 to Harris et al.). In the case of organic chloride as co-catalyst, HCl may be formed in situ in the reactor. However, the presence of HCl in the downstream product separation sections of the plant may corrode distillation columns and other equipment, especially if there is any water present. Accordingly it is important to avoid the introduction of water during ionic liquid catalyzed hydrocarbon conversion processes.
There is a need for a systematic startup procedure for ionic liquid catalyzed hydrocarbon conversion processes, including alkylation processes for alkylate gasoline manufacture, not only to optimize the process performance and efficiency, but also to increase plant reliability and prolong the useful life of the equipment.